U.S. patent application number 17/006038 was filed with the patent office on 2021-05-06 for system and method for measuring repetitive complex and pulse modulated rf signals.
The applicant listed for this patent is Keysight Technologies, Inc.. Invention is credited to Jean-Pierre Teyssier.
Application Number | 20210132141 17/006038 |
Document ID | / |
Family ID | 1000005074457 |
Filed Date | 2021-05-06 |
![](/patent/app/20210132141/US20210132141A1-20210506\US20210132141A1-2021050)
United States Patent
Application |
20210132141 |
Kind Code |
A1 |
Teyssier; Jean-Pierre |
May 6, 2021 |
SYSTEM AND METHOD FOR MEASURING REPETITIVE COMPLEX AND PULSE
MODULATED RF SIGNALS
Abstract
A method for measuring modulated radio frequency (RF) signals
from a device under test (DUT) includes inputting a test RF signal
to the DUT, where the test RF signal is modulated with a repetitive
complex waveform and a pulsed waveform, the repetitive complex
waveform including multiple RF tones with an RF tone spacing and an
RF repetition period, where a pulse width of the pulsed waveform is
less than the RF repetition period; acquiring an output RF signal
from the DUT responsive to the input test RF signal; down
converting the output RF signal to an intermediate frequency (IF)
signal; sampling the IF signal using an analog to digital converter
(ADC) having an ADC clock frequency; measuring ADC samples of the
IF signal; and reconstructing the test RF signal modulated with the
repetitive complex waveform using the measured ADC samples.
Inventors: |
Teyssier; Jean-Pierre;
(Santa Rosa, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Keysight Technologies, Inc. |
Santa Rosa |
CA |
US |
|
|
Family ID: |
1000005074457 |
Appl. No.: |
17/006038 |
Filed: |
August 28, 2020 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62928104 |
Oct 30, 2019 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01R 31/2822 20130101;
H04B 17/29 20150115; H04B 17/11 20150115; H04B 17/0085
20130101 |
International
Class: |
G01R 31/28 20060101
G01R031/28; H04B 17/11 20060101 H04B017/11; H04B 17/29 20060101
H04B017/29; H04B 17/00 20060101 H04B017/00 |
Claims
1. A method for measuring modulated radio frequency (RF) signals
from a device under test (DUT), the method comprising: inputting a
test RF signal to the DUT, wherein the test RF signal is modulated
with a repetitive complex waveform and a pulsed waveform, the
repetitive complex waveform comprising a plurality of RF tones with
an RF tone spacing and an RF repetition period, wherein a pulse
width of the pulsed waveform is less than the RF repetition period;
acquiring an output RF signal from the DUT responsive to the input
test RF signal; down converting the output RF signal to an
intermediate frequency (IF) signal; sampling the IF signal using an
analog to digital converter (ADC) having an ADC clock frequency;
measuring ADC samples of the IF signal; and reconstructing the test
RF signal modulated with the repetitive complex waveform using the
measured ADC samples.
2. The method of claim 1, wherein measuring the ADC samples
comprises accumulating measured ADC samples measured during
measurement periods substantially corresponding to consecutive
on-pulses of the pulsed waveform.
3. The method of claim 2, wherein measuring the ADC samples further
comprises concatenating a predetermined number of the measured ADC
samples to create a time record.
4. The method of claim 2, wherein measuring the ADC samples further
comprises discarding measured ADC samples measured during
non-measurement periods substantially corresponding to off-pulses
of the pulsed waveform, occurring between the on-pulses.
5. A method for measuring modulated radio frequency (RF) signals
from a device under test (DUT), the method comprising: inputting a
test RF signal to the DUT, wherein the test RF signal is modulated
with a repetitive complex waveform and a pulsed waveform, the
repetitive complex waveform comprising a plurality of RF tones with
an RF tone spacing F.sub.Mod and an RF repetition period T.sub.Mod;
acquiring an output RF signal from the DUT responsive to the input
test RF signal, wherein the output RF signal is modulated with the
repetitive complex waveform, comprising the RF tone spacing
F.sub.Mod and the RF repetition period T.sub.Mod, and the pulsed
waveform; down converting the output RF signal to an intermediate
frequency (IF) signal, wherein the IF signal is modulated with a
repetitive complex waveform comprising a plurality IF tones with an
IF tone spacing F.sub.IF and an IF repetition period T.sub.IF,
wherein the pulsed waveform of the test RF signal comprises
on-pulses, each of which is a fraction of the IF repetition period
T.sub.IF, and off-pulses, each of which is approximately an integer
multiple of the IF repetition period T.sub.IF; sampling the IF
signal using an analog to digital converter (ADC) having an ADC
clock frequency F.sub.ADC, wherein the RF tone spacing F.sub.Mod is
selected to equal a first fraction of the ADC clock frequency
F.sub.ADC, and wherein the IF tone spacing F.sub.IF is selected
such that the plurality of RF tones are down converted to the
plurality of IF tones which correspond to harmonics of a second
fraction of the ADC clock frequency F.sub.ADC, and the IF
repetition period T.sub.IF equals an integer multiple of the RF
repetition period T.sub.Mod; measuring ADC samples of the IF signal
during at least measurement periods, which substantially correspond
to the on-pulses of the pulsed waveform, respectively; and
concatenating a predetermined number of the ADC samples measured
during the measurement periods to create a time record.
6. The method of claim 5, wherein the time record has a length
equal to the IF repetition period T.sub.IF.
7. The method of claim 5, wherein the first fraction of the ADC
clock frequency F.sub.ADC is N/M (N and M being positive integers),
and the second fraction of the ADC clock frequency F.sub.ADC is
F.sub.ADC/M, such that the RF tone spacing F.sub.Mod is selected to
equal the ADC clock frequency F.sub.ADC times (N/M), and wherein
the plurality of IF tones correspond to the harmonics of
F.sub.ADC/M, and the IF repetition period T.sub.IF equals N times
the RF repetition period T.sub.Mod.
8. The method of claim 5, further comprising: when an RF bandwidth
of the output RF signal is wider than an IF bandwidth of the IF
signal, repeating acquisitions of the output RF signal to obtain
multiple IF signals at the IF bandwidth, and stitching the multiple
IF signals together to provide a stitched IF bandwidth
corresponding to the RF bandwidth.
9. The method of claim 5, wherein each of the measurement periods
equals the IF repetition period T.sub.IF divided by L (L being
positive integers).
10. The method of claim 9, wherein L is the predetermined number of
consecutive measurement periods that create the time record.
11. The method of claim 5, wherein ADC samples of the IF signal are
also measured during non-measurement periods, which substantially
correspond to the off-pulses of the pulsed waveform, respectively,
the method further comprising: discarding the ADC samples measured
during the non-measurement period.
12. The method of claim 11, wherein each of the measurement periods
equals the IF repetition period T.sub.IF divided by L, and each of
the non-measurement periods, occurring between the measurement
periods, equals the IF repetition period T.sub.IF multiplied by K
(L and K being positive integers).
13. A system for measuring modulated radio frequency (RF) signals
from a device under test (DUT), the system comprising: a signal
source configured to generate a test RF signal that is applied to
the DUT, wherein the test RF signal is modulated with a repetitive
complex waveform and a pulsed waveform, the repetitive complex
waveform comprising a plurality of RF tones with a tone spacing
F.sub.Mod and an RF repetition period T.sub.Mod; a local oscillator
(LO) configured to generate an LO signal having an LO frequency; a
mixer configured to mix the LO signal with an output RF signal,
received from the DUT in response to the applied test RF signal,
and to output an intermediate frequency (IF) signal modulated with
a repetitive complex waveform comprising a plurality of IF tones
with a tone spacing F.sub.IF and an IF repetition period T.sub.IF,
wherein the pulsed waveform of the test RF signal comprises
on-pulses, each of which is a fraction of the IF repetition period
T.sub.IF, and off-pulses, each of which is approximately an integer
multiple of the IF repetition period T.sub.IF; an analog to digital
converter (ADC) having an ADC clock frequency F.sub.ADC and
configured to sample the IF signal from the mixer, wherein the RF
tone spacing F.sub.Mod is selected to equal the ADC clock frequency
F.sub.ADC multiplied by N/M, N and M being positive integers, and
wherein the IF tone spacing F.sub.IF is selected such that the
plurality of RF tones are down converted to the plurality IF tones
which correspond to harmonics of the ADC clock frequency F.sub.ADC
divided by M, and the IF repetition period T.sub.IF equals N times
the RF repetition period T.sub.Mod; and a processing unit
programmed to measure ADC samples of the IF signal, and to
accumulate measured ADC samples measured during measurement periods
substantially corresponding to the on-pulses of the pulsed
waveform, and to concatenate a predetermined number of the
accumulated ADC samples to create a time record having a length
equal to the IF repetition period T.sub.IF.
14. The system of claim 13, wherein the processing unit is further
programmed to discard measured ADC samples measured during
non-measurement periods substantially corresponding to the
off-pulses of the pulsed waveform.
15. The system of claim 13, wherein the time record has a length
equal to the IF repetition period T.sub.IF.
16. The system of claim 13, wherein a first fraction of the ADC
clock frequency F.sub.ADC is N/M (N and M being positive integers),
and a second fraction of the ADC clock frequency F.sub.ADC is
F.sub.ADC/M, such that the RF tone spacing F.sub.Mod is selected to
equal the ADC clock frequency F.sub.ADC times (N/M), and wherein
the plurality of IF tones correspond to the harmonics of
F.sub.ADC/M, and the IF repetition period T.sub.IF equals N times
the RF repetition period T.sub.Mod.
17. The system of claim 14, wherein each of the measurement periods
equals the IF repetition period T.sub.IF divided by L, and each of
non-measurement periods equals the IF repetition period T.sub.IF
multiplied by K (L and K being positive integers).
18. The system of claim 17, wherein L is a predetermined number of
consecutive measurement periods that create the time record.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority under 35 U.S.C.
.sctn. 119(e) to U.S. Provisional Application No. 62/928,104 filed
on Oct. 30, 2019. The entire disclosure of U.S. Provisional
Application No. 62/928,104 is specifically incorporated herein by
reference in its entirety.
BACKGROUND
[0002] A device under test (DUT), such as various components of a
wireless communications device, may be characterized by stimulating
it with a repetitive complex modulated radio frequency (RF) signal,
which is also pulse modulated, and measuring a resulting output RF
signal. The measurements of the output RF signal may be used to
determine various parameters of the DUT, such as gain, delay and
distortion, for example. The measurements are made using a test
instrument, such as a vector network analyzers (VNA) or spectrum
analyzers (SA), which incorporates a superheterodyne receiver.
Generally, the superheterodyne receiver acquires the output RF
signal, down converts the output RF signal to a lower frequency
intermediate frequency (IF) signal, and digitizes the IF signal
before measuring the DUT parameters. The IF signal may be digitized
using an analog to digital converter (ADC), which samples the IF
signal at a lower rate than the modulation.
[0003] Conventionally, in order to perform measurements, a pulse
width of the pulse modulation must be greater than a repetition
period of the repetitive complex modulated RF signal. This is
because, when the pulse width is less than the repetition period,
the RF signal is chopped up, making it difficult to reconstruct and
measure the complex modulation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] The example embodiments are best understood from the
following detailed description when read with the accompanying
drawing figures. It is emphasized that the various features are not
necessarily drawn to scale. In fact, the dimensions may be
arbitrarily increased or decreased for clarity of discussion.
Wherever applicable and practical, like reference numerals refer to
like elements.
[0005] FIG. 1 is a simplified block diagram of a test system for
measuring parameters of a device under test (DUT) using a
repetitive complex and pulse modulated test radio frequency (RF)
signal, according to a representative embodiment.
[0006] FIG. 2A is a graph showing magnitude of a test RF signal
versus frequency, according to a representative embodiment.
[0007] FIG. 2B is a graph showing magnitude of an RF modulation
envelope of the test RF signal versus time, according to a
representative embodiment.
[0008] FIG. 3A is a graph showing magnitude of an IF signal versus
frequency, according to a representative embodiment.
[0009] FIG. 3B is a graph showing magnitude of an IF modulation
envelope of the IF signal versus time, according to a
representative embodiment.
[0010] FIG. 4 includes comparison graphs showing magnitude of an IF
signal and magnitude of an IF modulation envelope of the IF signal,
both plotted in the time domain, according to a representative
embodiment.
[0011] FIG. 5 is a simplified flow diagram showing a method for
measuring pulsed modulated RF signals from a DUT, according to a
representative embodiment.
DETAILED DESCRIPTION
[0012] In the following detailed description, for purposes of
explanation and not limitation, representative embodiments
disclosing specific details are set forth in order to provide a
thorough understanding of an embodiment according to the present
teachings. Descriptions of known systems, devices, materials,
methods of operation and methods of manufacture may be omitted so
as to avoid obscuring the description of the representative
embodiments. Nonetheless, systems, devices, materials and methods
that are within the purview of one of ordinary skill in the art are
within the scope of the present teachings and may be used in
accordance with the representative embodiments. It is to be
understood that the terminology used herein is for purposes of
describing particular embodiments only and is not intended to be
limiting. The defined terms are in addition to the technical and
scientific meanings of the defined terms as commonly understood and
accepted in the technical field of the present teachings.
[0013] It will be understood that, although the terms first,
second, third etc. may be used herein to describe various elements
or components, these elements or components should not be limited
by these terms. These terms are only used to distinguish one
element or component from another element or component. Thus, a
first element or component discussed below could be termed a second
element or component without departing from the teachings of the
present disclosure.
[0014] The terminology used herein is for purposes of describing
particular embodiments only and is not intended to be limiting. As
used in the specification and appended claims, the singular forms
of terms "a," "an" and "the" are intended to include both singular
and plural forms, unless the context clearly dictates otherwise.
Additionally, the terms "comprises", and/or "comprising," and/or
similar terms when used in this specification, specify the presence
of stated features, elements, and/or components, but do not
preclude the presence or addition of one or more other features,
elements, components, and/or groups thereof. As used herein, the
term "and/or" includes any and all combinations of one or more of
the associated listed items.
[0015] Unless otherwise noted, when an element or component is said
to be "connected to," "coupled to" or "adjacent to" another element
or component, it will be understood that the element or component
can be directly connected or coupled to the other element or
component, or intervening elements or components may be present.
That is, these and similar terms encompass cases where one or more
intermediate elements or components may be employed to connect two
elements or components. However, when an element or component is
said to be "directly connected" to another element or component,
this encompasses only cases where the two elements or components
are connected to each other without any intermediate or intervening
elements or components.
[0016] The present disclosure, through one or more of its various
aspects, embodiments and/or specific features or sub-components, is
thus intended to bring out one or more of the advantages as
specifically noted below. For purposes of explanation and not
limitation, example embodiments disclosing specific details are set
forth in order to provide a thorough understanding of an embodiment
according to the present teachings. However, other embodiments
consistent with the present disclosure that depart from specific
details disclosed herein remain within the scope of the appended
claims. Moreover, descriptions of well-known apparatuses and
methods may be omitted so as to not obscure the description of the
example embodiments. Such methods and apparatuses are within the
scope of the present disclosure.
[0017] FIG. 1 is a simplified block diagram of a test system for
measuring parameters of a DUT using a repetitive complex modulated
RF signal, which is also pulse modulated (referred to as "complex
and pulse modulated test RF signal" or "test RF signal"), according
to a representative embodiment.
[0018] Referring to FIG. 1, test system 100 includes an RF signal
source 110, an RF receiver 120 and a processing unit 130 configured
for testing a DUT 140. The RF receiver 120 may be included in a
test instrument, such as a vector network analyzer (VNA) or
spectrum analyzer (SA), for example, or any other test equipment
used for measuring modulated RF signals. The RF signal source 110
and/or the processing unit 130 may also be included in the test
instrument along with the RF receiver 120, or may be implemented as
separate devices that function in cooperation with the test
instrument. The DUT 140 may be any type of electronic device, such
as an amplifier, a mixer or a converter, for example, that provides
an output RF signal in response to a test RF signal (stimulus
signal) input by the RF signal source 110 to the DUT 140.
[0019] The RF signal source 110 and the RF receiver 120 may be
configured by and/or operated under control of the processing unit
130. For example, the processing unit 130 may be programed to
perform all or part of the steps discussed below with reference to
FIG. 4. In various embodiments, the processing unit 130 may be
implemented using one or more processors, such as a digital signal
processor (DSP) and/or a computer processor (collectively
"processor(s)"), application specific integrated circuits (ASICs),
field-programmable gate arrays (FPGAs), or combinations thereof,
using software, firmware, hard-wired logic circuits, or
combinations thereof. Processor(s), in particular, may be
constructed of any combination of hardware, firmware or software
architectures, and may include their own memory for storing
executable software/firmware or code that allows performance the
various functions. In an embodiment, the processor(s) may comprise
a central processing unit (CPU), for example, executing an
operating system.
[0020] Memory (not shown) may be provided in or with the processing
unit 130 in order to store software, code and/or programs
executable by the processor(s), as well as data, such as
measurement data, collected from the DUT 140 and the RF receiver
120, as well as other sources of information. The memory may be
implemented by any number, type and combination of random access
memory (RAM) and read-only memory (ROM), for example, and may store
various types of information, such as computer programs and
software algorithms executable by the processor(s) (and/or other
components), as well as raw data and/or testing and measurement
data storage, for example. The various types of ROM and RAM may
include any number, type and combination of computer readable
storage media, such as a disk drive, electrically programmable
read-only memory (EPROM), electrically erasable and programmable
read only memory (EEPROM), a compact disk (CD), a digital versatile
disk (DVD), a universal serial bus (USB) drive, registers, a
blu-ray disk, and the like, which are tangible and non-transitory
storage media (e.g., as compared to transitory propagating
signals).
[0021] The RF signal source 110 is configured to generate the
complex and pulse modulated test RF signal that is applied to the
DUT 140. The RF signal source 110 may be a vector signal generator,
for example. In particular, the RF signal source 110 modulates an
RF signal with a repetitive complex waveform and a pulsed waveform
to provide the complex and pulse modulated test RF signal. Because
the complex modulation is repetitive in the time domain, the test
RF signal will include multiple RF tones in the frequency domain.
The pulsed waveform of the test RF signal includes a series of
on-pulses separated by a series of off-pulses over time, where each
on-pulse may have a magnitude of one and each off-pulse may have a
magnitude of zero. In an embodiment, durations of the on-pulses are
shorter than durations of a repetition period of the repetitive
complex modulation.
[0022] As shown in FIGS. 2A and 2B, the repetitive complex waveform
modulating the test RF signal has an RF tone spacing (F.sub.Mod)
and an RF repetition period (T.sub.Mod). In particular, FIG. 2A is
a graph showing magnitude of the test RF signal, plotted in the
frequency domain, where the test RF signal includes representative
RF tones 221, 222, 223 and 224 that are separated from one another
by the RF tone spacing F.sub.Mod. FIG. 2B is a graph showing
magnitude of the test RF signal, plotted in the time domain, where
the RF modulation envelope of the test RF signal includes
representative RF repetition periods T.sub.Mod 241, 242 and 243.
The RF repetition period T.sub.Mod is equal to the inverse of the
RF tone spacing (1/F.sub.Mod). Also, pulse widths of the on-pulses
of the pulsed waveform are shorter in duration than the RF
repetition periods T.sub.Mod 241, 242 and 243 of the repetitive
complex modulated waveform.
[0023] The test RF signal is input to the DUT 140 as a stimulus
signal, in response to which the DUT 140 provides a repetitive
complex and pulse modulated output RF signal. The output RF signal
is modulated with the same repetitive complex waveform, having the
RF tone spacing F.sub.Mod in the frequency domain and the RF
repetition period T.sub.Mod in the time domain, and the same pulsed
waveform as the test RF signal. The output RF signal is acquired by
the RF receiver 120, which includes a mixer 121, an LO 122 and an
analog to digital converter (ADC) 123. The LO 122 generates an LO
signal at an LO frequency that is mixed with the output RF signal
by the mixer 121 to down convert the complex and pulse modulated
output RF signal to an intermediate frequency (IF) signal. The IF
signal is similarly complex and pulse modulated, having a
repetitive complex waveform, which includes multiple IF tones with
an IF tone spacing (F.sub.IF) in the frequency domain and an IF
repetition period (T.sub.IF) in the time domain.
[0024] Notably, each on-pulse of the pulsed waveform of the test RF
signal, discussed above, is a fraction of the IF repetition period
T.sub.IF and each off-pulse of the pulsed waveform is approximately
an integer multiple of the IF repetition period T.sub.IF. For
example, the on-pulse may have a duration of approximately
T.sub.IF/3, and the off-pulse may have a duration of approximately
2*T.sub.IF, although in practice, the durations of the on-pulses
and off-pulses may vary slightly from these ideal values. Other
combinations of on-pulse and off-pulse durations may be
incorporated, without departing from the scope of the present
teachings.
[0025] The ADC 123 samples the IF signal output by the mixer 121
according to an ADC clock frequency (F.sub.ADC). In various
implementations, the sampled IF signal may be digitally processed
(e.g., by the processing unit 130) to appear as though the IF
signal were sampled at a different rate than a fixed ADC clock
frequency of the ADC 123, which is referred to as "re-sampling."
The embodiments herein may include sampling at the fixed ADC clock
frequency or at a re-sampled ADC clock frequency, without departing
from the scope of the present teachings. Accordingly, the term ADC
clock frequency F.sub.ADC as used herein is intended to include
both the fixed ADC clock frequency and any re-sampled ADC clock
frequencies that may be used.
[0026] The modulation of the test RF signal provided by the RF
signal source 110 is based on the ADC clock frequency F.sub.ADC.
That is, the RF tone spacing F.sub.Mod of the test RF signal (and
thus the output RF signal) is selected to equal a first fraction of
the ADC clock frequency F.sub.ADC, where the first fraction may be
represented by F.sub.ADC*N/M (N and M being positive integers). The
complex modulation of the IF signal provided by the mixer 121 is
likewise based on the ADC clock frequency F.sub.ADC and also the LO
frequency of the LO signal. That is, the LO frequency of the LO
signal is selected so that the RF tones of the output RF signal are
down converted to a grid of frequencies (IF tones) that correspond
to harmonics of a second fraction of the ADC clock frequency
F.sub.ADC, where the second fraction of the ADC clock frequency
F.sub.ADC is F.sub.ADC/M (M being a positive integer). This
simplifies digital filtering requirements of the digitized IF
signal following the ADC 123, and allows the ADC samples to be used
as a timing reference for measuring the IF signal. The IF
repetition period T.sub.IF of the IF signal equals an integer
multiple of the RF repetition period T.sub.mod. That is, the IF
repetition period T.sub.IF=N*T.sub.Mod=M/F.sub.ADC (N and M being
positive integers). Thus, the IF repetition period TT may be the
exact ADC acquisition time required to capture a complete time
record of the output RF signal in the time domain, as discussed
below.
[0027] In an embodiment, when the bandwidth of the test RF signal
(and thus the output RF signal) is wider than the IF bandwidth of
the RF receiver 120, then multiple output RF signal acquisitions
are performed using different LO settings of the LO 122,
respectively, to obtain corresponding IF signals. The frequency
domain results of the IF signals, measured using time records as
described herein, may be stitched together to represent the full
output RF signal bandwidth.
[0028] FIG. 3A is a graph showing magnitude of an IF signal,
plotted in the frequency domain, according to a representative
embodiment, and FIG. 3B is a graph showing magnitude of an IF
modulation envelope of the IF signal, plotted in the time domain,
according to a representative embodiment.
[0029] Referring to FIG. 3A, the IF signal includes representative
IF tones 321, 322, 323 and 324 that are consecutively separated
from one another by the IF tone spacing F.sub.IF. The IF tone
spacing is based on the ADC clock frequency F.sub.ADC. That is the
IF tone spacing F.sub.IF is equal to F.sub.ADC/M, such that the IF
tones correspond to harmonics of F.sub.ADC/M, and thus harmonics of
the RF tone spacing F.sub.Mod of the test RF signal, as well. This
is apparent in the depicted example of FIG. 3A in that every third
IF tone (e.g., IF tones 321 and 324) overlaps with an RF tone
(e.g., RF tones 221 and 222), which is the case for example when
N=M=3. Referring to FIG. 3B, the IF modulation envelope includes
representative IF repetition periods T.sub.IF 341, 342 and 343. As
mentioned above, each of the IF repetition periods T.sub.IF 341,
342 and 343 is equal to M/F.sub.ADC, which in the depicted example
is 3/F.sub.ADC. Of course, other values of M and/or N may be
incorporated without departing from the scope of the present
teachings.
[0030] FIG. 4 includes comparison graphs showing magnitude of an IF
signal and magnitude of an IF modulation envelope of the IF signal,
both plotted in the time domain, according to a representative
embodiment.
[0031] Referring to FIG. 4, the test RF signal is pulse modulated
by a pulsed waveform that is aligned with the repeating complex
modulated IF signal, as indicated by representative IF repetition
periods T.sub.IF 341, 342, 343, 344, 345 and 346. The
representative pulsed waveform includes on-pulses 401, 402 and 403,
and off-pulses 411 and 412 separating the on-pulses 401, 402 and
403. The duration (pulse width) of each of the on-pulses is
approximately equal to T.sub.IF/L, and the duration of each of the
off-pulses is approximately equal to T.sub.IF*K (L and K being
positive integers), where the on-pulses are shorter than the
off-pulses. That is, the actual durations of the on-pulses 401, 402
and 403 may be slightly longer than the ideal values (T.sub.IF/L)
depicted in FIG. 4, and the actual durations of the off-pulses 411
and 412 may be slightly shorter than the ideal values (T.sub.IF*K)
depicted in FIG. 4, for example. However, the sum of the actual
duration of an on-pulse (e.g., on-pulse 401) and an adjacent
off-pulse (e.g., off-pulse 411) still equals one period of the
pulsed waveform (on-pulse+off-pulse=T.sub.IF/L+T.sub.IF*K).
Generally, the on-pulses 401, 402 and 403 being approximately equal
to T.sub.IF/L means that they have durations within 15 percent of
T.sub.IF/L, and the off-pulses 411 and 412 being approximately
equal to T.sub.IF*K means that they have durations within 15
percent of T.sub.IF*K. In the depicted example, L=3 and K=2, such
that each of on-pulses 401, 402 and 403 has a duration of
approximately T.sub.IF/3, and each of the off-pulses 411 and 412
has a duration of approximately T.sub.IF*2. Of course, other
combinations of on-pulse and off-pulse durations may be
incorporated, without departing from the scope of the present
teachings.
[0032] The sampling and measurements of the IF signal by the ADC
123 are substantially time aligned with the pulsed waveform
initially provided by the RF signal source 110 for pulse modulating
the test RF signal, as discussed below. That is, the sampling is
performed during measurement periods that substantially correspond
to the on-pulses and non-measurement periods that substantially
correspond to the off-pulses. The duration of each of the
measurement periods is equal to T.sub.IF/L and the duration of each
of the non-measurement periods is equal to T.sub.IF*K (L and K
being positive integers). Measurements made by the ADC 123 during
the measurement periods (substantially corresponding to the
on-pulses 401, 402 and 403) are accumulated, and measurements made
by the ADC 123 during the non-measurement periods (substantially
corresponding to the off-pulses 411 and 412) are discarded.
Alternatively, the ADC 123 may be configured to stop performing
measurements during the non-measurement periods, as opposed to
performing and discarding the measurements. The measurement periods
and non-measurement periods are said to substantially correspond to
(or be substantially time aligned with) the on-pulses and
off-pulses because the actual durations of the on-pulses and
off-pulses of the pulsed waveform may vary from T.sub.IF/L and
T.sub.IF*K, respectively, by up to 15 percent, as discussed above.
Accordingly, substantially correspond (and substantially time
aligned) means that the measurement periods and non-measurement
periods are within 15 percent of being time aligned with the
on-pulses and off-pulses, respectively.
[0033] The accumulated measurements of the ADC samples from L
consecutive measurement periods are concatenated together in the
time domain to create a complete time record 441 of length T.sub.IF
(representing one cycle of the IF signal). Thus, in the depicted
example, the time record 441 consists of three (L=3) consecutive
sets of measured samples from three consecutive measurement
periods, which substantially correspond to the three consecutive
on-pulses 401, 402 and 403.
[0034] As discussed above, the test RF signal is effectively a
combination of a repetitive complex modulated signal and a pulse
modulated signal, which do not need to be time aligned. Likewise,
the pulsed waveform of the pulse modulated signal and the
measurements by the ADC 123 do not need to be time aligned with
(and/or triggered by) the repetitive complex modulated signal.
However, the pulsed waveform of the pulse modulated signal and the
measurements by the ADC 123 do need to be substantially time
aligned with one another. Also, the measurements by the ADC 123
included in each time record 441 provide all the timing information
needed for reconstructing the repetitive complex modulated waveform
of the test RF signal over each of the IF repetition periods
T.sub.IF in the IF signal. This approach can handle arbitrarily
wide RF modulation bandwidths, as it is compatible with frequency
domain stitching, as mentioned above.
[0035] FIG. 5 is a simplified flow diagram showing a method for
measuring modulated RF signals from a DUT, according to a
representative embodiment. All or some of the steps shown in FIG. 5
may be implemented by the processing unit 130. For example, a
non-transitory computer readable medium may have stored thereon
software instructions that, when executed by processor(s) of the
processing unit 130, cause these processor(s) to measure output RF
signals from the DUT in accordance with FIG. 5.
[0036] Referring to FIG. 5, a test RF signal is generated by a
signal source (e.g., RF signal source 110) in block S511, and input
to a DUT (e.g., DUT 140) in block S512. The test RF signal is
modulated with a repetitive complex waveform and a pulsed waveform.
The repetitive complex modulated waveform includes multiple RF
tones with an RF tone spacing F.sub.Mod in the frequency domain and
an RF repetition period T.sub.Mod in the time domain. The pulse
modulated waveform includes a series of on-pulses separated by a
series of off-pulses, the respective lengths of which are
determined based anticipated characteristics of an IF signal,
discussed below with reference to block S514. Pulse widths of the
on-pulses of the pulsed waveform are shorter in duration than the
RF repetition period T.sub.Mod of the repetitive complex modulated
waveform. Also, the RF tone spacing F.sub.Mod of the repetitive
complex modulated waveform in the test RF signal is determined
based on an ADC clock frequency of an ADC used to sample and
digitize this IF signal, discussed below with reference to block
S515.
[0037] In block S513, an output RF signal is acquired from the DUT
via an RF receiver (e.g., RF receiver 120). The output RF signal is
responsive to the input test RF signal, and characterizes features
of the DUT, e.g., for testing purposes. The output RF signal
acquired from the DUT is modulated with the same repetitive complex
waveform and pulsed waveform as the test RF signal, including the
RF tone spacing F.sub.Mod and the RF repetition period
T.sub.Mod.
[0038] In block S514, the output RF signal is down converted to an
IF signal by mixing the output RF signal at a mixer (e.g., mixer
121) with an LO signal provided by an LO (e.g., LO 122). The IF
signal is likewise modulated with a repetitive complex waveform
that includes multiple IF tones with an IF tone spacing F.sub.IF
and an IF repetition period T.sub.IF. As mentioned above, the pulse
timing of the pulsed waveform modulating the test RF signal is
determined based on the characteristics of the IF signal. In
particular, the length of each of the on-pulses of the pulsed
waveform is a fraction of the IF repetition period T.sub.IF, and
the length of each of the off-pulses of the pulsed waveform is an
integer multiple of the IF repetition period T.sub.IF. For example,
each of the on-pulses may have a length equal to T.sub.IF/L, and
each of the off-pulses mat have a length of T.sub.IF*K (L and K
being positive integers).
[0039] The IF signal is sampled and digitized in block S515 using
an ADC (e.g., ADC 123) that has an ADC clock frequency F.sub.ADC.
As mentioned above, the RF tone spacing F.sub.Mod of the repetitive
complex waveform modulating the test RF signal, as generated by the
signal source, is determined based on the ADC clock frequency
F.sub.ADC. In particular, the RF tone spacing F.sub.Mod is selected
to equal a first fraction of the ADC clock frequency F.sub.ADC,
where the first fraction of the ADC clock frequency F.sub.ADC may
be represented by N/M (N and M being positive integers). With
regard to the IF signal provided in block S514, the IF tone spacing
F.sub.IF is selected such that the RF tones of the test RF signal
provided in block S511 are down converted to the IF tones, such
that the IF tones correspond to harmonics of a second fraction of
the ADC clock frequency F.sub.ADC, where the second fraction of the
ADC clock frequency F.sub.ADC may be represented by F.sub.ADC/M (M
being a positive integer). Also, the IF repetition period T.sub.IF
of the IF signal is an integer multiple of the RF repetition period
T.sub.Mod, which may be represented by N*T.sub.Mod or M/F.sub.ADC
(N and M being positive integers).
[0040] In block S516, samples of the IF signal measured by the ADC
are accumulated only during measurement periods, which
substantially correspond to the on-pulses of the pulsed waveform.
Measurements made by the ADC during intervening non-measurement
periods, which substantially correspond to the off-pulses, are
discarded. A predetermined number of the measured samples
accumulated from the measurement periods are concatenated in block
S517 in order to create time records (e.g., time record 441),
respectively. The measured samples in each time record may be
accumulated from consecutive measurement periods, substantially
corresponding to consecutive on-pulses. Each of the time records is
equal in length to the length of the IF repetition period T.sub.IF
of the IF signal, representing one cycle of the IF signal. For
example, as discussed above, each of the measurement periods may
have a length equal to T.sub.IF/L (L being a positive integer).
Therefore, concatenating measurements corresponding to L
consecutive measurement periods provides a time record having the
length L*T.sub.IF/L, or simply T.sub.IF.
[0041] Using the time records from block S516, the non-pulsed
repetitive complex waveform may be reconstructed, e.g., by the
processing unit 130, over each of the IF repetition periods
T.sub.IF in the IF signal, where the time records provide all of
the necessary timing information. Also, as mentioned above, the
repetitive complex waveform and the pulsed waveform do not need to
be time aligned. Unlike conventional techniques, the method enables
measurement of repetitive complex modulated and pulse modulated RF
signals that have pulse widths that are shorter than the repetition
periods of the complex modulation, thus expanding the types of RF
signals that can be measured.
[0042] While the invention has been illustrated and described in
detail in the drawings and foregoing description, such illustration
and description are to be considered illustrative or exemplary and
not restrictive; the invention is not limited to the disclosed
embodiments.
[0043] Other variations to the disclosed embodiments can be
understood and effected by those having ordinary skill in the art
in practicing the claimed invention, from a study of the drawings,
the disclosure, and the appended claims. In the claims, the word
"comprising" does not exclude other elements or steps, and the
indefinite article "a" or "an" does not exclude a plurality. The
mere fact that certain measures are recited in mutually different
dependent claims does not indicate that a combination of these
measures cannot be used to an advantage.
[0044] While representative embodiments are disclosed herein, one
of ordinary skill in the art appreciates that many variations that
are in accordance with the present teachings are possible and
remain within the scope of the appended claim set. The invention
therefore is not to be restricted except within the scope of the
appended claims.
* * * * *